The present invention relates to downhole drilling assemblies, specifically downhole drilling assemblies for use in oil, gas, geothermal, and horizontal drilling. Drilling fluid may comprise any of a number of liquid and gaseous fluids and mixtures of fluids and solids used in operations to drill boreholes into the earth. In these operations, drilling fluid may remove cuttings from the well, control formation pressures, seal permeable formations, maintain wellbore stability, and minimize formation damage.
Controlling the drilling fluid's weight may contribute to maintaining the stability of the wellbore. As formation pressures increase, the drilling fluid's weight may also be increased to maintain the wellbore's integrity. However, in some situations, where the drilling fluid's weight exerts a pressure against the formation that is significantly lower than the formation pressure, the formation's pressure may cause the well bore to collapse. The prior art discloses applications where drilling fluid weight has been altered to contribute to drilling applications.
U.S. Patent Publication No. 2005/0284641 to Watkins et al., which is herein incorporated by reference for all that it contains, discloses a variable density fluid for wellbore operations and a method of drilling a wellbore using a variable density fluid where the density of the fluid changes by design as a function of external parameters which vary along the depth or length of the well. The variable density of the fluid is beneficial for controlling sub-surface pressures within desirable pore pressure and fracture gradient envelopes. The variability of fluid density permits construction and operation of a wellbore with much longer hole sections than when using conventional single gradient fluids.
U.S. Pat. No. 4,103,749 to Erickson et al., which is herein incorporated by reference for all that it contains, discloses a centrifugal cleaner powered by a turbine. Both the centrifugal cleaner and turbine are downhole in a housing at the end of a drill string. A branch of a drilling mud stream is cleaned of solid matter by the centrifugal cleaner. A branch of the clean fluid drives the turbine of the centrifugal cleaner. A second branch of the clean fluid does useful work at the downhole location, such as erosive drilling of bore hole rock. Turbine exhaust, cleaner exhaust and drilling mud combine and flow into the rock erosion zone to clear it of chips formed by the drilling. Fluid from this zone passes up the annulus between the bore hole and the drill string.